LV CB Open time with electronic trip for arc flash
LV CB Open time with electronic trip for arc flash
(OP)
For a LV molded case circuit breaker, equipped with electronic trip unit, the tripping curves may only include the trip unit time, but may not include the CB opening time thereafter. Has anyone seen manufacturer's data on this? The application is arc flash analysis.






RE: LV CB Open time with electronic trip for arc flash
With electronic trip units, you have to make sure you are using the curve for the appropriate type of breaker (molded case vs insulated case vs power circuit breaker). There will be separate TCCs for each type of breaker even though the trip unit model sounds identical.
David Castor
www.cvoes.com
RE: LV CB Open time with electronic trip for arc flash
RE: LV CB Open time with electronic trip for arc flash
If the TCC references "Total Clearing Time", that has to include the breaker clearing time as well as the trip unit time.
David Castor
www.cvoes.com
RE: LV CB Open time with electronic trip for arc flash
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RE: LV CB Open time with electronic trip for arc flash
Also, the TCC is for a particular circuit breaker with a particular trip unit - not for the trip unit alone.
What is your consultant seeing on this TCC that indicates the times do not include the breaker time?
I don't see anything unusual about this TCC that would change my opinion. Let us know if C-H says something different.
David Castor
www.cvoes.com
RE: LV CB Open time with electronic trip for arc flash
RE: LV CB Open time with electronic trip for arc flash
RE: LV CB Open time with electronic trip for arc flash
The trip time for an (external to the breaker) 'arc flash protective device' that uses a shunt trip to trip the breaker will be different from trip time for the RMS trip system that is shown on the curve you are referencing.
So..it may be that DPC and your consultant are both right.